This invention relates generally to marine structures, and more particularly to a cathodic protection system for controlling corrosion of such structures.
Known marine structures such as oil and gas structures typically include a platform which is supported above sea level by an arrangement of steel legs anchored on or driven into the sea bed, and coupled together by steel truss members. If unprotected, seawater will rapidly corrode such steel structures.
Accordingly, it is well known to apply cathodic protection to steel marine structures by providing sacrificial anodes, for example of aluminum or zinc, which are electrically coupled to the steel structure. The anodes preferentially corrode to produce an electrical current that protects the steel structure from corrosion.
Often the sacrificial anodes take the form of many individual masses which are attached directly to the legs and/or truss members of the structure. Installation of such anodes, or replacement at the end of their useful life, requires the efforts of a diver. Offshore structures may be set in waters far beyond the practical diver working depth of about 91 m (300 ft.), for example about 366 m (1200 ft.). Maintenance or replacement of anodes at such depths requires the use of underwater remotely operated vehicles (ROVs), which are very expensive.
It is also known that sacrificial anodes can be configured in a vertical column supported by the marine structure, similar to a tubing string. These columns are configured to be attached to the marine structure using special brackets. By attaching the columns, additional weight is added to the marine structure and there is a limit to the number of columns that can be physically installed. Furthermore, this type of column may not be suitable for retrofit situations where the marine structure was not designed to carry the weight of the anodes, and where the specific brackets needed to attach a vertical anode column were not included in the initial construction of the marine structure.